This invention relates to actuators of the electromagnetic type and, more particularly, to electromagnetic actuators in which the travel of the movable armature is adjustable.
Electromagnetic actuators have been used for a wide variety of purposes. One type that has been used in a number of applications is a so-called voice coil or moving coil motor. In motors of this type, when a current is applied to a coil positioned in a magnetic field, with a segment of the coil perpendicular to the field, a force is exerted on the coil segment. The direction of this force is dependent upon the direction of current flow and the direction of the magnetic field.
Another kind of conventional electromagnetic actuator is referred to commonly as a solenoid. To date a wide variety of useful solenoids have been proposed for performing a multitude of functions. In such solenoids reverse polarization of coil windings will result in reverse axial translation of a magnetically permeable armature disposed within the core of the winding. U.S. Pat. Nos. 1,361,935 and 3,940,726 are representative of such kinds of solenoids. Still another type of electromagnetic actuator is described in commonly-assigned U.S. Pat. Nos. 3,868,712 and 4,008,448 issued, respectively, to C. Biber and J. Muggli. Electromagnetic actuators of this type have been found to be extremely useful for driving shutter blades, in a photographic apparatus. In such apparatus, it is desired to have the shutter blades accurately displaced by a plunger of the actuator for desired exposure control. However, in the camera assembly process, seldom are the shutter blades and the electromagnetic actuator joined together in such a fashion that the travel of the actuator plunger will result in the desired shutter blade displacement. Accordingly, the actuator must be adjusted to provide for the correct plunger travel.
One known approach for adjusting the stroke of the plunger is through use of an adjustable plug. More specifically, the plug is threadedly connected to the coil assembly of the actuator and has one end which contacts and limits plunger movement. To adjust the stroke of the plunger, the plug is threadedly advanced inwardly or outwardly with respect to the coil assembly. However, use of threaded plugs gives rise to problems in obtaining optimum actuator performance. This is because threaded connections usually have air gaps between otherwise complementary threaded surfaces. Such gaps add undesirably to the magnetic impedance of the system and results in a less efficient actuator.
Besides, actuators of the last-noted type have plungers which are susceptible of being dislodged easily therefrom. This adds to problems of camera assembly especially when the plunger is to be coupled to the shutter blades.